Current Modifications
I had been looking at dyno charts from automotive engines
that were almost identical to mine and noticed that they were making about 25hp
more than I was at 4000 rpms. The only difference I could find was better
induction and exhaust systems.
I started exploring the idea by removing the existing intake
“U” tube and made two short manifolds that connected to the heads. Using these
manifolds, I ground tested various dual carb setups, the largest set being a
pair of Mikuni 41mm slide carbs. While I was not seeing any improvements at
static rpms, I was able to confirm that it would idle just fine.
A new tuned intake manifold and exhaust system was designed using formulas derived from documentation on the subject,
but there was simply not enough space under the cowl for them. Tuning for 4000 rpms, the four tubes that would run to each intake port would have been 16.4" long tapering from 1.7" at the plenum to to 1.5" at the head. The plenum chamber required a volume of 1450cc's.
Turbocharger
Still wanting to
improve fuel distribution and increase power, I continued
to ponder the dilemma. Shortly after, I was speaking with Joe Horvath from Revmaster
Aviation about using dual Revflow carbs mounted to two short runners when the
subject of turbochargers came up. Joe mentioned that he thought he still had
most of the parts to put a complete system together. We discussed it for a
while and I ended up purchasing a Rayjay turbo and various other parts, most of
which would not fit under the cowl and were ultimately not used.
The turbo is a Rayjay "B" flow 300 series that was used on the 150hp turbo Corvair cars. Its the smallest of the 300 series and weights about 12 pounds. The 300 series uses a positive (carbon) seal assembly enabling it to be used in a "draw through"configuration with the carb mounted before the turbo allowing the use of a carb without modifications.
Exhaust
The exhaust was constructed from 1.625" mild steel and welded with gas. I attempted to incorporate a small flex coupler in each primary pipe. I was not able to get them to seal after welding using gas or wire feed.
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| Flex coupling installation which was ultimately removed. |
The flex couplings were abandoned and thick silicone exhaust gaskets were used at an intermediate point in each primary to allow for some movement of the pipes.
After welding and cleanup, the pipes were coated inside and out with a 2000f ceramic coating to reduce heat within the cowl and prolong their life. Not counting the weight of the turbo, the exhaust weighs 16 lbs.
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| Exhaust componants after ceramic coating |
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| Completed and installed exhaust system |
Since the system is a draw through, a waste gate is not required as power is controlled by the carb's butterfly. I have purchased an external waste gate and may use it in the future, but for now I want to see if I can avoid adding the extra weight and complexity.
Carburetor
Many hours were burned searching for a carb that met my goals. The Mikuni SBN was selected because of its tuneability, performance, size, lack of a float bowl, capability of in flight mixture control and price. Details can be found on another blog post here: http://schmleff.blogspot.com/2013/04/alternative-carbs-mikuni-sbn.html
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| Mikuni SBN and custom bracket to allow the use of a standard throttle cable and TPS sensor |
Fuel System
Since the carb requires about 4 psi of fuel pressure, a redundant pump system was incorporated using two Facet fuel pumps plumbed in parallel. More details found here: Fuel System
Electrical System
Since the aircraft now requires electrical power to fly, A dual battery system with the ability to isolate each was used. The aircraft did not have a charging system so a 35a alternator was installed, as well as a starter for convince.
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| Electrical system schematic |
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| Converted UPS batteries provide 240 CCA |
Ignition System
I have been flying for years with a single mag. It failed
once during my flight testing phase, at about 45hrs total time on the mag.
After that, I took it apart and performed a "factory" overhaul on it.
I have never been worried about it failing in flight.
A programable secondary ignition was installed for a number of reasons. With the ability to run the engine above sea level pressure, the ignition timing advance needs to be reduced as boost levels rise to prevent detonation. Being fully programable, the ignition system also allows for greater efficiency at lower power settings. A few added benefits are redundancy, data logging, electronic waste gate control and various GPIO functions.
I dug around and priced dozens of systems and settled on the
CB Performance Magnaspark crank fired ignition kit. For $559, its not much more
than a fixed ignition secondary and can do a whole lot more: http://www.cbperformance.com/ProductDetails.asp?ProductCode=2094 (for what its worth, don't tell them that its for an airplane ; )
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| The ignition system ties into many parts of the other systems |
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| Magna Spark crank fired digital ignition |
The 36-1 crank wheel that comes with the kit was not usable with an aircraft conversion and one that would sandwich between the prop flange and extension was designed and laser cut.
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| Custom crank wheel |
When it came time to build a timing table for the system, I found little guidance as to what an aircraft ignition table look like. To get my head around what is happening in different phased of a typical flight, I built color coded (by phase of flight) spreadsheet and filled in the manifold pressure and RPM's I expected to see.
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| Timing table exercise |
Using the CAFE foundation's papers on ignition and many automotive air-cooled VW timing tables, I eventually settled on a conservative table using the latest advance of 30 degrees under full power.
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| Initial timing table |
The ignition logs various parameters for later analysis. It has been very useful in the testing process.
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| Log file from a high power test run |
Turbo Scavenging Pump
After multiple test runs with various fixes, it became
obvious that a gravity drain from the turbo was just not going to work. I already had a 4
gear dry sump oil pump but was not ready to invest the time to
dry sump the entire oil system. What I did was convert the pump to use the
larger set of gears to feed oil to the engine and the smaller set to pull oil
from the turbo. This video gives an overview of the pump and covers what is
required to convert the pump.
Engine Build
After the initial testing of the engine and systems were completed, the engine was torn down for inspection and modification.
- Changed cylinder heads to Revmaster Aviation's 049 heads with hemispherical combustion chambers and evenly spaced dual spark plugs
- Changed the camshaft from an Engle-100 to an Engle TCS-10 turbo grind
- Installed Total Seal gapless rings
- Revised dipstick and tube to allow for better cooling baffle shape
- Removed unnecessary protrusions from the sides of the engine case to allow for better cooling baffle sealing
- Reduced the compression ratio to 7.5:1
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| Large valves and hemispherical combustion chambers are used in the Revmaster 049 heads |
Induction System
This is one of the systems that I will likely redo in the future. Space and time were getting tight while I was trying to get the airplane ready for the 2013 Airventure Cup race. It is functional, but not as efficient as I would like.
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| The induction system incorporating both filtered cool air and carb heat |
Cowl Modifications
The cowl was revised and extended forward to reduce drag, allow space for the ignition's VR sensor's and to allow for better cooling baffle diffusers. These topics are covered in detail starting at this link (and newer posts): Cowl Mods
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| Using splines, sheetrock tape and lightweight filler to make a plug |
Cooling System
As mentioned, the longer cowl provided more room for divergent ducts to feed the cooling baffles. More information about the baffles can be found here: Cooling Baffle Design and Construction
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| Preparing to make the left side cooling inlet flange |
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| Glass over foam was used to make room for the oil cooler and ductwork |
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| Foam blocks being glued between the oil cooler and the inlet area |
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| Completed oil cooler duct |
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| Removable oil cooler inlet rings |
Seat and Control System Redesign
With the sheer number of new modifications with a number of them having not been tried before (like the use of a Mikuni SBN on a 4-stroke airplane engine), I decided to make space to fit a helmet on while testing. Doing so required that the seat and control system be revised. More information about these modifications can be found here: Revised Control System
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| Old (top) and new control system functional drawings |
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| Single piece pillow blocks getting a grease groove cut |
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| Completed control system before installation |
What's Left?
My goal was to have all of these modifications completed and test flown before the Mojave Fly-in, but I simply ran of out time. The right side cooling baffle and baffle seals and a few cleanup details remain. After the last few months of little sleep, its time for a break. Work should resume soon and it should be back in the air shortly!
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